Modelling Runoff and Sediment Yield Delivered from Floodplain Mining Activities to the Madre de Dios River

Abstract:

The Madre de Dios River is located in the southern Peruvian Amazonia. Driven by the rising increasing gold prices, high demand for informal markets, and lack of government control, artisanal and small-scale gold mining (ASGM) has been developed in the area since the 1980s. Remote sensing analysis demonstrates that over the last 30 years, ASGM has been responsible for around 95,750 ha (over 236 600 acres) of deforestation. Together with ASGM, deforestation and land use cover changes have caused irreversible effects in the watershed hydrologic conditions, and the resulting runoff and sediment generation (potentially contaminated with mercury) have adversely affected the morphology, water quality, and aquatic habitat of the Madre de Dios River and its main tributaries (Colorado, Inambari, Tambopata and Los Amigos rivers).

The U.S. Department of Agriculture's Soil and Water Assessment Tool (SWAT) model has been adopted to develop simulations to evaluate the impact of land use cover changes due to deforestation. This study aims to find out how the effects of artisanal and small-scale gold mining have changed the hydrodynamics and geomorphology of the Madre de Dios River and its main tributaries. Thus, the goals of this study are: (1) the change in floodplain sediment yield as a result of runoff increase and (2) the resulting sediment loads of Colorado and Inambari rivers. The results of preliminary simulations with the SWAT model show that from 2001 to 2018, the increase of land cover change resulted in the gradual rise of sediment concentration, mainly in the Colorado and Inambari rivers, due in part to increased deforestation in their floodplain areas. This study could provide a better understanding of the hydrological characteristics of the Madre de Dios basin, which combined with knowledge on the amount of sediment delivered by ASGM, would prove useful for future studies on the transport and fate of mercury.